Composition and method for inhibiting corrosion

ABSTRACT

A composition and method of inhibiting corrosion and white rust on metal components in a water system. The composition preferably comprises an amino-acid based polymer (most preferably a polyaspartic acid or a salt thereof), hydroxyphosphonoacetic acid, and a second phosphonic acid (preferably a phosphonocarboxylic acid), and does not require the use of regulated metals. The composition is effective even in the presence of biocides. A preferred method of inhibiting white rust comprises adding an amino-acid based polymer or hydroxyphosphonoacetic acid or both to the water system. A preferred method of inhibiting corrosion or white rust comprises adding an amino-acid based polymer, hydroxyphosphonoacetic acid, and a phosphonocarboxylic acid to the water system. Preferably the active concentrations are at least 3 ppm each of the amino-acid based polymer and hydroxyphosphonoacetic acid when added to a volume of water in the water system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/322,616 filed on Apr. 14, 2016 and U.S. Provisional ApplicationSer. No. 62/363,574 filed on Jul. 18, 2016.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to a treatment composition and method forinhibiting corrosion or white rust on metal components in water systems.This invention is particularly useful in the corrosive environmentsfound in low LSI (Langelier Saturation Index) water systems, such asopen recirculating systems, closed loop cooling or heating systems, andboilers.

2. Description of Related Art

Various water treatment compositions are used to reduce corrosion,mineral scale, and white rust formation on metal components in contactwith an aqueous solution in water systems such as open recirculatingsystems, closed loop cooling or heating systems, cooling towers andboilers, and help protect the metal components of these systems. Themetals typically used in these water systems include ferrous metals,including galvanized steel, aluminum and its alloys, copper and itsalloys, lead, and solder. Many known corrosion inhibitors containregulated toxic metals, such as zinc, chromate, and molybdate, which areharmful to the environment and increase the costs. Zinc is typicallyused as corrosion inhibitor in water systems with highly corrosive water(low LSI). However its usage is undesirable due to toxicity issues andits use faces regulations in some locations. Tin has also been used as anon-toxic alternative to zinc, but it is more expensive.

The performance of many known corrosion inhibitors is also negativelyimpacted by the use of biocides, which are frequently used in watersystems to control the growth of microorganisms. The use of polyasparticacid and a single phosphonic acid are disclosed in U.S. Pat. No.5,523,023 as effective in inhibiting corrosion, even in the presence ofa biocide when the phosphonic acid is2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC). The preferredphosphonic acid in the '023 patent is PBTC, but other phosphonic acids,including 1-hydroxyethane 1,1-disphosphonic acid andhydroxyphosphonoacetic acid (HPA) are also mentioned as suitable. Thecorrosion rate results shown in the '023 patent based on the use ofpolyaspartic acid and PBTC are better than other corrosion inhibitors,but there is still a need for even greater corrosion inhibition,particularly in the presence of biocides.

Currently utilized solutions for white rust prevention includepassivating the metal surfaces with zinc carbonate and control of waterchemistry to reduce potential for white rust formation. Known treatmentsinclude the use of inorganic phosphates, thiocarbamates,organo-phosphorous compounds and tannins. For example, U.S. Pat. Nos.5,407,597 and 6,468,470 disclose compositions comprisingorganophosphorus compounds (including PBTC), an alkali metal salt ofmolybdenum, titanium, tungsten, or vanadium, and either a carbamatecompound or a tannin compound. U.S. Pat. No. 6,183,649 discloses awhite-rust treatment composition comprising PBTC, sodium polyacrylate,sodium tolytriazole, an alkali metal molybdate, and an alkali metalbromide for treating circulating water systems. The '649 patent alsodiscloses the addition of a 1.5% aqueous solution of decylthioethyletheramine (DTEA) at a rate of 251b/1,000 gallons of water/weekto the circulating water system prior to adding the white rust treatmentcomposition at a rate of 600 ppm per cycle for ten cycles ofrecirculation after addition of the DTEA.

There is a need for an effective corrosion inhibitor and an effectivewhite rust inhibitor composition and method that are moreenvironmentally friendly and capable of adequately performing inconjunction with biocides. There is also a need for a single treatmentcomposition and method that will address both corrosion and white rustwithout the need for separate treatments, which may negatively interactwith each other.

SUMMARY OF THE INVENTION

According to one preferred embodiment of the invention, an improvedcorrosion inhibitor and white rust inhibitor composition comprises anamino-acid based polymer (AAP), hydroxyphosphonoacetic acid (HPA) or itswater soluble salt, and another phosphonic acid or its water solublesalt. Hydroxyphosphonoacetic acid has the following general structure:

Most preferably, the amino-acid based polymer is polyaspartic acid orits water soluble salt, but other compounds such as polyglycine acid,polyglutamic acid and their salts may also be used. Most preferably, theamino acid based polymer has the following formula:

where R1=H, R2=OH, and R3=COOH and x=1 for polyaspartic acid. Mostpreferably, the other phosphonic acid is a phosphonocarboxylic acid orany organic phosphonate may also be used. Most preferably, thephosphonocarboxylic acid is 1-hydroxyethane-1,1-diphosphonic acid (HEDP)or 2-phosphonobutene-1,2,4-tricarboxylic acid (PBTC) orphosphonosuccinic acid. Preferably the weight ratio of AAP to HPA in theinhibitor composition is 90:10 to 10:90 and the ratio of combined AAPand HPA to other phosphonic acid is in the range of 90:10 to 60:40. Morepreferably, the weight ratio range of AAP to HPA in the inhibitorcomposition is 80:20 to 80:20 and the ratio of combined AAP and HPA toother phosphonic acid is 80:20 to 70:30.

Most preferably, a composition according to a preferred embodiment ofthe invention is all organic and does not contain regulated metals suchas zinc, chromate, and molybdate and its performance is not affected byaddition of biocides. Most preferably, a composition according to apreferred embodiment of the invention does not contain tin.

It was previously known to use both HPA and AAP, such as polyasparticacid, separately as corrosion inhibitors. It was also disclosed in the'023 patent that AAP could be used together with phosphonocarboxylicacid to inhibit corrosion, but it was not previously known to use AAPand HPA together along with another phosphonic acid, preferably aphosphonocarboxylic acid, or an organic phosphonate to inhibitcorrosion.

When added to the water in the water system being treated, a preferredcomposition according to the invention yields at least 3 ppm active AAP,at least 3 ppm active HPA, and at least 2 ppm of the other phosphonicacid. More preferably, when added to the water in the water system beingtreated, a preferred composition yields 3 ppm-50 ppm AAP, 3 ppm-50 ppmHPA, and 2 ppm-20 ppm of the other phosphonic acid and most preferablybetween 5 ppm-30 ppm AAP, 3 ppm-20 ppm HPA, and 2 ppm-10 ppm of theother phosphonic acid. Additionally, the combined total of the threecomponents of a preferred composition yields at least 8 ppm activecorrosion inhibitors when added to the water being treated. Theseingredients have the unexpected synergistic effect of improved corrosioninhibition without requiring the use of toxic metals and without beingadversely impacted by biocides.

In addition to unexpected and synergistic effect of the inhibitorcomposition on ferrous metal corrosion inhibition in low LSI water, thesame composition also has a positive effect on preventing formation ofwhite rust on galvanized steel. Galvanized steel consists of a thincoating of zinc fused to a steel substrate. White rust is a rapid,localized corrosion attack on zinc that usually appears as a voluminouswhite deposit. This rapid corrosion can completely remove zinc in alocalized area with the resultant reduction in equipment life. Neitherhydroxyphosphonoacetic acid nor amino-acid based polymers, such aspolyaspartic acid, alone or in combination, has been previously utilizedin commercial products for white rust prevention. Without being bound bytheory, it is believed that the compositions according to the inventionmay be forming a protective layer on the surface of galvanized steel andreduce white rust formation. For treating white rust according to theinvention, it is preferred to use hydroxyphosphonoacetic acid, anamino-acid based polymer, and another phosphonic acid in the amountsindicated above for inhibiting corrosion (both weight ratios andconcentrations when added to the water in the water system beingtreated), but it has also been found that the use of an amino-acid basedpolymer without hydroxyphosphonoacetic or the other phosphonic acid isbeneficial at inhibiting white rust. According to another preferredembodiment, a composition for treating white rust comprises anamino-acid based polymer and hydroxyphosphonoacetic acid, withoutanother phosphonic acid. According to yet another preferred embodiment,a composition for treating white rust comprises an amino-acid basedpolymer, without any hydroxyphosphonoacetic acid.

According to other preferred embodiments, compositions for inhibitingcorrosion or white rust also comprise one or more of the followingingredients: a neutralizing amine, chlorine stabilizer, such asmonoethanol amine (MEA); a scale inhibitor and dispersion agent, such aspolycarboxylate polymer and/or carboxylate/sulfonate functionalcopolymers (typical examples: polyacryclic acid (PAA), polymethacrylicacid (PMAA), polymaleic acid (PMA), and copolymers of acrylic acidsulfonated monomers, such as AA/AMPS); other scale and corrosioninhibitors, chelant agents; azole corrosion inhibitors, such asbenzotriazole, alkylbenzotriazole (tolyltriazole); and/or a fluorescentdye tracer, such as 1,3,6,8-Pyrenetetrasulfonic acid tetrasodium salt(PTSA). The overall composition preferably comprises around 2%-15% (byweight) of an amino-acid based polymer (such as polyaspartic acid),around 2% to 10% (by weight) of hydroxyphosphonoacetic acid, and around2% to 10% (by weight) of another phosphonic acid.

According to one preferred method of preventing corrosion of metalcomponents and/or white rust on galvanized steel components in a watersystem, a treatment composition according to the preferred embodimentsof invention as described above is added to the water system. For acomposition combining one or more of the AAP, HPA, and anotherphosphonic acid as described above, a preferred method comprises feedingthe composition into the water at an effective feed rate of 20 ppm-600ppm, or more preferably 100-300 ppm, of treatment composition, dependingon the treated water chemistry and the amount of optional components inthe treatment composition. Preferably, a sufficient amount of treatmentcomposition is added to the water system to provide effective activeamounts of one or more of the three treatment components (depending onwhether corrosion or white rust is being treated or both) of at least 3ppm AAP, at least 3 ppm HPA, and at least 2 ppm of another phosphonicacid, each as concentrations when added to the volume of water in thewater system being treated. More preferably, the treatment compositionis added in a sufficient amount to provide effective active amounts oneor more of the components of between 3 ppm-50 ppm AAP, between 3 pm-50ppm HPA, and between 2 ppm-20 ppm of another phosphonic acid when addedto the water in the water system. Most preferably, these effectiveactive amounts are 5 ppm-30 ppm AAP, 3 ppm-20 ppm HPA, and 2 ppm-10 ppmother phosphonic acid when added to the water in the water system.

BRIEF DESCRIPTION OF THE DRAWINGS

The composition and method of the invention are further described andexplained in relation to the following figures wherein:

FIG. 1 contains photographs showing corrosion levels on steel couponsafter spinner tests at flow rates of 3 ft/sec and 5 ft/sec;

FIG. 2 contains photographs showing corrosion levels on steel couponsafter spinner tests run in presence of biocide at flow rates of 3 ft/secand 5 ft/sec;

FIG. 3 contains photographs showing corrosion levels on steel couponsafter spinner tests at a flow rate of 3 ft/sec; and

FIG. 4 contains photographs showing white rust levels on galvanizedcoupons after spinner tests.

DESCRIPTION OF PREFERRED EMBODIMENTS

Several lab tests were run to test the effectiveness of variouscompositions according to the invention. Compositions according to theinvention were evaluated using spinner tests to simulate flowing waterover metal components in a water system. Each spinner test set-upcomprises a stainless steel container of water with four metal coupons(mild steel coupons (C1010) and copper coupons (CDA 11) were used)suspended in the water in each container from holders hanging from arotating shaft. The shaft rotates the coupons in the water in thestainless steel container at 147 rotations/min, representing a flow rateof 3-5 ft/s, depending on coupon distance from center of the rotatingshaft. The initial volume of water used in each spinner test wascharacteristic of corrosive, low hardness water typically found in watersystems. The water used had the characteristics shown in Table 1 below.

TABLE 1 Low hardness, corrosive water used in Spinner test experimentsCharacteristic Value Unit pH 8 to 8.5 Conductivity 220 cP Ca Hardness 30ppm, (as CaCO3) Mg Hardness 10 ppm, (as CaCO3) Chlorides, Total 25 ppmCl M Alkalinity 30 ppm, (as CaCO3) Sulfate, Total 28 ppm, as SO4

During each spinner test the water is aerated and maintained at constanttemperature of 120 F and constant volume (any evaporation is compensatedwith automatic addition of deionized water when water level drops belowsensor level). Standard test duration is 48 hours.

Using the spinner test set-up, compositions according to preferredembodiments of the invention (Example Nos. 1-3 including AAP, HPA, andanother phosphonic acid—HEDP) without any added zinc or tin (as shown inTable 2) were compared to compositions using only zinc (Comp. Ex. 4),only tin (Comp. Ex. 5), only AAP (Comp. Ex. 6), only HPA (Comp. Ex. 7),HPA combined with tin (Comp. Ex. 8), and AAP combined with tin (Comp.Ex. 9) (all as shown in Table 3) as the primary inhibitor(s). The ppmconcentrations of the various treatments are concentrations when addedto the volume of water in the spinner test container. The compositionswith zinc or tin were for comparison to those without. Zinc is typicallyused as corrosion inhibitor in water systems with highly corrosive water(low LSI). However its usage is undesirable due to toxicity issues andits use face regulations in some locations. Tin has been promoted andpatented as a non-toxic alternative to zinc, but it is more expensive.In addition to the primary corrosion inhibitor components listed inTables 2 and 3, all of the tests were carried out in the presence 4 ppmactive AA/AMPS copolymer and 4 ppm active TTA. These ingredients wereadded to the water in each spinner test set-up to provide thoseconcentration levels. The corrosion and pitting level for mild steelcoupons after spinner tests in presence of different inhibitors arepresented in FIG. 1.

TABLE 2 Corrosion inhibitor compositions according to the inventionInhibitor Unit Example 1 Example 2 Example 3 AAP (amino acid based ppm7.5 5.2 5.2 polymer - such as a active* commercially available watersolution containing about 40% of sodium salt of polyaspartic acid) HPAppm 2.5 5.0 5.0 (hydroxyphosphonoacetic active acid) HEDP ppm 3 3 3active MEA ppm 0.25 1.0 Zn (zinc) ppm N/A N/A N/A active Sn (tin) ppmN/A N/a N/A active *ppm active refers to the amount of active rawmaterial, in contrast to ppm which refers to the weight of raw materialin mg/L. For example, HPA is commercially available as a 50% watersolution, so adding 10 ppm raw material will provide 5 ppm active HPA.

TABLE 3 Corrosion inhibitor compositions - Comparative Examples Inhib-Comp. Comp. Comp. Comp Comp. Comp. itor Unit Ex 4 Ex 5 Ex 6 Ex 7 Ex 8 Ex9 AAP ppm 15 7.5 active HPA ppm 5 5 active HEDP ppm 3 3 3 3 3 3 activeMEA ppm Zn ppm 1 active Sn ppm 1 1 0.5 active

Spinner tests were run with each composition at a flow rate equivalentto around 3 ft/second and at a flow rate equivalent to around 5ft/second. A control test, without any treatment was also carried outfor comparison. FIG. 1 shows photographs of a representative mild steelcoupon after each spinner test with the control and with ExampleComposition Nos. 1-9. The amount of corrosion and pitting on the couponsis shown in the photographs. As can be seen, the control coupons showextensive corrosion (dark areas on photographs). The coupons used withcompositions according to preferred embodiments of the invention (Ex.Nos. 2-3) show little, if any, corrosion or pitting (very few dark areason photographs). The coupons used with Ex. No. 1, which contains allthree components according to a preferred embodiment of the inventionfor corrosion inhibition, but only contains 2.5 ppm HPA (less than themore preferred amount of at least 3 ppm), shows improved results overthe control and the comparative examples (Comp. Nos. 4-9), but showsslightly more corrosion than Ex. Nos. 2-3, where 5 ppm of HPA was used.The coupons used with the comparative compositions (Comp. Nos. 4-9) aresignificantly better than the control, but do show evidence of corrosionand pitting that is greater than with Ex. Nos. 1-3. Based on theresults, it appears that the combination of AAP, HPA, and anotherphosphonic acid (in these examples, HEDP) interact synergistically toprovide improved corrosion control, without requiring the use of zinc,tin or other regulated metals.

Some prior art water treatment corrosion inhibition compositions do notprovide effective protection when oxidizing biocides are used in thesame system to prevent biological growth. The most widely used oxidizingbiocides are chlorine and stabilized bromine. Additional spinnercorrosion tests were carried out using Example compositions Nos. 2 and 3compared to comparative Example compositions Nos. 4 (zinc only) and 7(HPA only) in the presence of a stabilized bromine biocide composition(commercially available as Chem-Aqua 42171). Example compositions 4 and7 were selected because they showed the best results in the spinnertests of the comparative examples. Both Comp. Ex. Nos. 4 and 7 performfairly well in low LSI water, but as discussed below, significantlyworse when biocide is added. Also, Comp. Ex. No. 4 is based on zinc,which is undesirable to use due to toxicity concerns. As with the priortests, these tests were carried out in presence 4 ppm active AA/AMPScopolymer and 4 ppm active TTA. A slug dose of 40 ppm of biocide wasadded at the beginning of each spinner test (after the corrosioninhibition composition was added and the test started) to yield about 1ppm FHR (free halogen residue).

FIG. 2 shows photographs of a representative mild steel coupon aftereach spinner test with the Example Compositions in the presence ofbiocide. As can be seen, the coupons used with compositions according topreferred embodiments of the invention (Ex. Nos. 2-3) show little, ifany, corrosion or pitting, indicating that the functionality ofpreferred compositions according to the invention is not negativelyaffected by a biocide. The coupons used with the comparativecompositions (Comp. Ex. Nos. 4 and 7) show substantially more corrosionthan with Ex. Nos. 2-3. It is noted that Comp. No. 7 was the use of HPAand HEDP, without any AAP, which showed good results without biocide,but significantly more corrosion occurred when a biocide was added. Thecomparative composition having AAP and HEDP, without any HPA, (Comp. Ex.No. 6) did so poorly without biocide (FIG. 1 above) that it was nottested with biocide because the results would be expected to be evenworse than in FIG. 1. Based on the results, it appears that thecombination of AAP, HPA, and another phosphonic acid together interactsynergistically to provide improved corrosion control even in thepresence of a biocide and show improved results over the use of HPAalone.

Corrosion rates for the mild steel coupons were also measured andcalculated from weight loss of the coupons. The results of both thespinner tests without added biocide and with added biocide aresummarized in Table 4. Information on corrosion mode, particularly thepresence of pitting (which is important in many applications and somecorrosion inhibitors, including HPA used alone, are known to be poorprotectors against pitting), is also included in Table 4. Mostpreferably, corrosion inhibitor compositions according to theembodiments of the invention achieve corrosion rates of 3 MPY or lessfor corrosion, even in the presence of a biocide.

TABLE 4 Corrosion Rates form spinner test experiments Mild Steel CouponCorrosion Rate, MPY [mil/yr] Low Hardness Water Low Hardness Water +Pitting Biocide Test 3 ft/sec 5 ft/sec Scale 3 ft/sec 5 ft/sec PittingControl 370 243 N/A Example 1 2.7 2.5 None Example 2 2.9 2.4 None 2.22.0 None Example 3 2.5 2.5 None 2.7 2.4 None Comp. Ex 4 2.7 2.7 Limited8.0 11 Sever pitting Comp. Ex 5 4.0 4.6 Pitting Comp. Ex 6 13.6 8.2Severe pitting Comp. Ex 7 2.6 3.2 Limited 6.4 5.7 Severe pitting Comp.Ex 8 3.9 5.2 Pitting Comp. Ex 9 3.8 3.2 Sever pitting Pitting scaledescription: None = no pitting observed Limited = few (1-5) pitts percoupon, usually very shallow Pitting = significant number of pits oncoupons (5-50) Sever pitting = a large number of pits (>50), usuallydipper and larger

Compositions according to preferred embodiments of the invention containorganic phosphate from the HPA and from the other phosphonic acid usedin these examples (HEDP). In the presence of a biocide, the organicphosphate is often reverted to orthophosphate, which is not as good inpreventing corrosion and also may cause issues with forming calciumphosphate scale. When the combination of AAP,HPA, and HEDP (or anotherphosphonic acid) is used as a corrosion inhibitor according to apreferred embodiment of the invention, virtually no reversion of organicphosphate to orthophosphate was detected. Samples from compositionExample Nos. 2 and 3 and comparative Example No. 7 were tested for thepresence of orthophosphates upon mixing of the composition and againafter 48 hours. The results are listed below in Table 5. Example Nos. 2and 3, which use AAP, HPA, and HEDP (and contain AA/AMPS and TTA asnoted above), showed very little orthophosphate increase over the 48hour period, but comparative Example No. 7 which contains HPA and HEDP(and contains AA/AMPS and TTA as noted above), but no AAP, showed asubstantial increase.

TABLE 5 Orthophosphate levels in low hardness test water in presence ofbiocide during the spinner corrosion test Orthophosphate (ppm PO4) TestInitial 48 hr (End of Test) Example 2 0.4 0.5 Example 3 0.2 0.4 Comp. Ex-7 0.3 1.6

According to another preferred embodiment, a water treatment compositionas listed in Table 6 (which is the same as Ex. 2 tested above) iseffective at inhibiting corrosion in a water system over a broad rangeof LSI values and in the presence of a biocide.

TABLE 6 Active %* in Component Wt % Composition Sodium polyasparte (AAP)13.0 5.2% as AAP Hydroxy phosphonoacetic Acid (HPA) 10.0 5.0% as HPA1-Hydroxyethylidene 1,1- 5.25 3.0% as PO4 diphosphonic acid (HEDP)Monoethanolamine (MEA) 1.0 0.99% Copolymer of acrylic acid andsulfonated 8.78 3.9% as monomer (AA/AMPS) AA/AMPS Tolyltriazole (TTA)9.40 4.0% as TTA 1,3,6,8-Pyrenetetrasulfonic acid tetrasodium salt 1.001% as PTSA (PTSA) NaOH or KOH 15.00 N/A Deionized water 36.57 N/A*Active % refers to active weight percent. Wt % is raw material weightpercent. Most of the raw materials are aqueous solutions and containonly a certain amount of solids that is the actual chemical component.The amount of active (Active %) is calculated based on raw materialweight percent and the amount of the chemical in the solution per theinformation provided by the supplier. For example, a commercial productmay be a 40% solution of AAP in water, so if 13% of of that product isused, the active is calculated as: 0.13*0.40*100% = 5.2% of AAP (actualchemical) in the formula

NaOH and/or KOH is preferably also added to the composition according toan embodiment of the invention. These ingredients are typically added towater treatment formulations in order to neutralize acid and to bringthe pH of the final composition to the desired level. Most of thecompositions will have pH>8, some will have pH>12. In compositions whereTTA is used (as with a preferred embodiment of a composition accordingto the invention) it is desirable to have higher pH (>11) for thecomposition in order to ensure solubility of TTA, which has very poorsolubility at lower pH.

Additional spinner tests in low LSI water were carried out in order totest the effectiveness of various concentrations of treatmentcompositions for inhibiting corrosion according to preferred embodimentsof the invention. The same spinner test parameters and low LSI water(Table 1) described above were used for these tests. The concentrationsof the ingredients when added to the spinner test water and the resultsof these tests are shown below in Table 7. FIG. 3 shows photographs ofthe test coupons (tested at a flow rate of 3 ft/sec) for eachcomposition after the test was completed.

TABLE 7 Additional Spinner Test Compositions & Results Comp. Comp. Comp.Comp. Inhibitor Unit Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16Ex. 17 AAP ppm 2.6 5.2 7.8 5.0 10 10 5.0 5.0 active HPA ppm 2.5 5.0 7.52.5 5 2.5 5.0 5.0 active AAP:HPA 51:49 51:49 51:49 67:33 67:33 80:2051:49 51:49 Ratio HEDP ppm 1.6 3.26 4.7 3.26 3.26 3.26 active (1.5 (3(4.4 (3 (3 (3 ppm ppm ppm ppm ppm ppm PO₄) PO₄) PO₄) PO₄) PO₄) PO₄) PBTCppm 2.6 active (0.95 ppm PO₄) MEA ppm 0.5 1 0.5 TTA ppm TTA 4 4 4 4 4 44 4 AA/AMPS ppm 4 4 4 4 4 4 4 4 Copolymer active Corrosion Results fromSpinner Test (low LSI water), mild steel (C1010) coupons at 3 ft/secflow rate Corrosion MPY 5.2 2.3 1.5 3.1 2.2 3.5 2.1 3.3 Rate* (mil/yr)Pitting Pitting none none none none none none None *Average for 2coupons from the same spinner test pot at 3 ft/sec

Comparative Examples 10, 13, and 15 use AAP, HPA, and HEDP but inamounts less than the preferred concentrations. These examples showincreased corrosion (and Comp. Ex. 10 showed moderate pitting) at lowlevels of the inhibitors. Example Nos. 11-12, 14, and 16 according topreferred embodiments of the invention show good performance (lowcorrosion rate and no pitting) for different optional components andvarying concentrations and ratios of AAP to HPA. The examples also showthat the change from HEDP to PBTC (Ex. 16) and reduction of secondarychelates does not affect the corrosion inhibition performance ofcompositions according to preferred embodiments of the invention.Example No. 17 used AAP and HPA, without a second phosphonic acid,similar to the composition described in the '023 patent. It showsimproved results in controlling corrosion in low LSI water, but theresults are not as good as in the examples according to preferredembodiments of the invention.

Additional spinner tests were conducted to compare compositions usingAAP and PBTC as disclosed in the '023 patent with compositions accordingto preferred embodiments of the invention. The test set-up was the sameas described above using low LSI water, mild steel (C1010) coupons, anda flow rate of 3 ft/sec. The results are shown in Table 8 below.

TABLE 8 Comparing Compositons Using One Phosphonic Acid to CompositionsUsing Two Phosphonic Acids Comp. Comp. Example 18 Example 19 Example 1280:20 40:60 (same as in Inhibitor Unit PBTC/AAP PBTC/AAP Example 20Example 21 Table 7) PBTC ppm 16 8 4.8 8 active HEDP ppm 4.7 active AAPppm 4 12 7.8 4 7.8 active HPA ppm 7.5 8 7.5 active TTA ppm 4 4 4 4 4 TTAAA/AMPS ppm 4 4 4 4 4 Copolymer active Corrosion MPY 3.1 3.1 1.9 1.7 1.5Rate* (mil/yr) Pitting none none none none None *Average for 2 couponsfrom the same pot at 3 ft/sec

As can be seen, the examples according to preferred embodiments of theinvention (Example Nos. 20, 21, and 12) with AAP, HPA, and a secondphosphonic acid (HEDP or PBTC) show much beter corrosion inhibitionresults than the comparatve examples using only AAP and PBTC (withoutany HPA). It is also noted that Comp. Ex. Nos. 18-19 resulted incorrosion rates greater than 3 MPY even when using 20 ppm totalinhibitor (AAP and PBTC), which is higher than the corrosion rateachievable with preferred compositions according to the invention usingsubstantially less total inhibitor, such as Example No. 11, which had acorrosion rate of 2.3 MPY using only 13.5 ppm total inhibitors (AAP,HPA, HEDP), and Example No. 16, which had a corrosion rate of 2.1 MPYusing only 12.6 ppm total inhibitors (AAP, HPA, PBTC). Additionally, thecorrosion rates of Comp. Ex. Nos. 18-19 are comparable to those in Comp.Ex. Nos. 13 and 15, which use AAP, HPA, and a second phosphonic acid,but the total amount of inhibitor needed to achieve the results in Comp.Ex. Nos. 18-19 (20 ppm total) is much higher than that needed in Nos. 13and 15 (10.76 and 15.76 ppm total, respectively). The results of theseexperiments show that the addition of a second phosphonic acid, incombination with AAP and HPA, provides an unexpected synergistic effectthat improves corrosion inhibition even when less total inhibitor isused and even in the presence of a biocide.

Those of ordinary skill in the art will understand that other sutiableor equivalent chemical compounds and other treatment compounds,including other corrosion inhibitors, may be substituted for any of theabove ingredients or added to any of the above ingredients within thescope of this invention. Compositions according to the embodiments ofthe invention are effective in inhibiting corrosion on metal componentsin water systems over a broad range of LSI values, including LSI<0, andwithout requiring the use of regulated toxic metals. These compositionsare also effective at higher pH values (7-9) typically found in watersystems, such as cooling towers and boilers, whereas some prior artinhibitors are ineffective or their effectiveness is reduced at such pHlevels (for example, a polyaspartic acid/stannous salt treatment iseffective only at pH 5-7). These compositions according to the inventionalso prevent reversion of organic phosphate to orthophosphate tomaintain effectiveness in the presence of a biocide.

Other experiments using an electrochemical method were conducted to testcompositions according to the invention for white rust prevention. Theresults in Table 9 below show synergistic effect of combining HPA andAAP (without another phosphonic acid) in reducing white rust formationas compared to use of each individual component (HPA alone and AAPalone). The cyclic voltammetry test was conducted in 0.1M sodiumcarbonate solution using zinc electrode. The measure of oxidation is thearea under the oxidation curve peak observed; the lower the area theless oxidation occurs, meaning lower corrosion rate. The results are theaverages of 6-10 experiments with standard deviation.

TABLE 9 Concentration Measure of Oxidation Inhibitor [ppm active][Coulombs*10⁻³] AAP 50 1.2 ± 0.2 HPA 50 1.0 ± 0.1 AAP/HPA (1:1 ratio)25:25 0.8 ± 0.1

Additional spinner corrosion tests were carried out in stainless steelcontainers in high alkalinity water known to form white rust ongalvanized surfaces to test the effectiveness of compositions accordingto preferred embodiments of the invention for the prevention of whiterust formation. The water chemistry, characteristic of high alkalinitysynthetic water, in these tests is detailed in Table 10 below. Four HotDip Galvanized steel coupons (HDG G70) with dimensions 1.0×4.0×0.02 inwere installed in each container on the holders hanging from a rotatingshaft that rotates at 147 rotations/min that represents flow rate of 3-5ft/s, depending on coupon distance from center of the rotating shaft.During the tests the water was aerated and maintained at constanttemperature of 120 F and constant volume (any evaporation wascompensated with automatic addition of DI water when the water leveldropped below a sensor level). Standard test duration was 48 hours. Theactive ingredients used in two comparative examples and three examplesof preferred compositions according to the invention, along withcorrosion rates, are listed in Table 11.

TABLE 10 High alkalinity/no hardness water used in Spinner testexperiments for white rust prevention Characteristic Value Unit pH8.7-8.9 Conductivity 2300 cP Ca Hardness 0 ppm, (as CaCO3) Mg Hardness 0ppm, (as CaCO3) Chlorides, Total 250 ppm Cl M Alkalinity 200 ppm, (asCaCO3) Sulfate, Total 500 ppm, as SO4

TABLE 11 Active Ingredients Composition and Galvanized Coupon CorrosionRate Comp. Ex. 22 - No Comp. Inhibitor Unit Inhibitor Ex. 23 Ex. 24 Ex.25 Ex. 26 AAP ppm — — 15 7.5 15 active HPA ppm — 7.5 7.5 2.5 — activeHEDP ppm — 3.26 3.26 3.26 3.26 active (3 ppm (3 ppm (3 ppm (3 ppm PO₄)PO₄) PO₄) PO₄) TTA ppm — 4 4 4 4 TTA AA/AMPS ppm — 4 4 4 4 Copolymeractive Corrosion Results- Galvanized Coupons (HDG G70) Corrosion MPY53.7 24.3 9.9 14.0 10.7 Rate* (mil/yr) *Average for 4 coupons from thesame pot (two at 3 ft/sec and two at 5 ft/sec flow rate)

In order to calculate the corrosion rate using the weight loss method,the galvanized coupons from these tests were cleaned according tostandard procedure by immersing coupons in concentrated ammonium acetateand rinsing. FIG. 4 shows photographs of the galvanized coupons afterthe spinner tests with the compositions described in Table 12, bothbefore and after cleaning. The white deposit visible on the couponsbefore cleaning is white rust. The damage of the galvanized layer due tocorrosion, shown as dark spots, is visible on the coupons aftercleaning. The blank (Comp. Ex. 22—No Treatment) coupon was completelycovered in white deposit and after cleaning most of the galvanized layerwas removed with visible mild steel corrosion. The coupon treated withHPA and HEDP without an amino-acid based polymer (Comp. Ex. 23) showedsubstantial white rust formation, but was still a great improvement overthe control (Comp. Ex. 22). Significantly better results were obtainedwith compositions in Examples 24-26. The best results were achieved withEx. 24 using AAP, HPA at greater than 3 ppm, and a second phosphonicacid (HEDP). Although the use of HPA is important in inhibiting mildsteel corrosion, its use is optional for white rust treatment. As can beseen from Example 26, the results of using AAP and HEDP without HPA werealmost as good as the three combined. Accordingly, a preferredcomposition for treating white rust according to the invention comprises2-15% amino-acid based polymer, 0-10% HPA, and 0-10% of a secondphosphonic acid. Preferably, the amount of active amino-acid basedpolymer in a treatment composition according to the invention is atleast 3 ppm, more preferably 3 ppm-50 ppm, and most preferably 5 ppm-30ppm, all as concentrations when added to the volume of water in thewater system being treated. More preferably, the AAP is used inconjunction with HPA in an amount of at least 3 ppm, more preferablyfrom 3 ppm-50 ppm, and most preferably from about 3 ppm-20 ppm and/oranother phosphonic acid in an amount of at least 2 ppm more preferablyfrom 2 ppm-20 ppm, and most preferably from about 2 ppm-10 ppm.

For treating white rust according to the invention, it is preferred touse both hydroxyphosphonoacetic acid and an amino-acid based polymer,and more preferably in conjunction with a second phosphonic acid, in theweight range amounts indicated above, but it has also been found thatthe use of an amino-acid based polymer or hydroxyphosphonoacetic withoutthe other is beneficial at inhibiting white rust.

According to one preferred method of preventing corrosion of metalcomponents and/or white rust on galvanized steel components in a watersystem, a treatment composition according to the invention as describedabove is added to the water system at a preferred effective feed rate of20 ppm-600 ppm, or more preferably 100-300 ppm, of treatment compositiondepending on the treated water chemistry and the amount of optionalcomponents in the treatment composition. Preferably, a sufficient amountof treatment composition is added to the water system to provideeffective active amounts of AAP of at least 3 ppm and of HPA of at least3 ppm, both as concentrations when added to the volume of water in thewater system being treated. More preferably, the amount of HPA is atleast 3 ppm. More preferably, the treatment composition is added in asufficient amount to provide effective active amounts of AAP between 3ppm-50 ppm, HPA between 3 ppm-50 ppm, and a second phosphonic acidbetween 2 ppm-20 ppm when added to the water in the water system. Mostpreferably, these effective active amounts are 5 ppm-30 ppm AAP, 3ppm-20 ppm HPA, and a second phosphonic acid between 2 ppm-10 ppm whenadded to the water in the water system. For treating white rust, the useof HPA is optional, so the treatment composition used in a preferredmethod according to the invention may comprise AAP without any HPA andbe added in amounts sufficient to provide these same concentrationranges of AAP in the water of the water system being treated. Accordingto another preferred embodiment, the composition added to the watersystem comprises a fluorescent tracer so that the level of compositionin the water system can be measured and monitored. Additional treatmentcomposition is added to the water system as needed, based on the tracermeasurements, to maintain an effective amount of treatment within thewater system.

All ppm concentrations of the various treatments in the example testsdescribed herein are concentrations when added to the water in thespinner test, to correlate to the concentrations when added to the waterin the water system being treated. Unless specifically excluded, allreferences to acids herein and in the claims include water soluble saltsof the acid, as will be understood by those of ordinary skill in theart. Those of ordinary skill in the art will also appreciate uponreading this specification, including the examples contained herein,that modifications and alterations to the preferred embodiments of thecomposition and method for using the composition to treat water may bemade within the scope of the invention and it is intended that the scopeof the invention disclosed herein be limited only by the broadestinterpretation of the appended claims to which the inventor is legallyentitled.

What is claimed:
 1. A method of treating water systems containing avolume of water to inhibit white rust formation on galvanized steelcomponents in the water system, the method comprising: adding anamino-acid based polymer to the water in the water system; and adding afirst phosphonic acid or its water soluble salt to the water in thewater system.
 2. The method of claim 1 wherein the adding steps providean active concentration of 3 ppm-50 ppm of the amino-acid based polymerand an active concentration of 3 ppm-50 ppm of the first phosphonic acidor its water soluble salt in the volume of water in the water system;wherein no tin is added to the water in the water system; and whereinthe water has a total hardness of 60 ppm or less CaCO₃.
 3. The method ofclaim 1 further comprising adding a second phosphonic acid or its watersoluble salt to the water in the water system; and wherein the firstphosphonic acid is hydroxyphosphonoacetic acid.
 4. The method of claim 3wherein both the amino-acid based polymer and hydroxyphosphonoaceticacid or its water soluble salt are added in amounts that when added to avolume of water in the water system provides a combined activeconcentration of the amino-acid based polymer, hydroxyphosphonoaceticacid or its water soluble salt, and second phosphonic acid or its watersoluble salt of at least 9 ppm in the water system; and wherein theweight ratio of the combined amino-acid based polymer andhydroxyphosphonoacetic acid or its water soluble salt to the and secondphosphonic acid or its water soluble salt is 90:10 to 60:40.
 5. Themethod of claim 3 wherein the second phosphonic acid is aphosphonocarboxylic acid or its water soluble salt.
 6. The method ofclaim 3 wherein the second phosphonic acid adding step provides anactive concentration of at least 2 ppm of the phosphonocarboxylic acidor its water soluble salt in a volume of water in the water systemwherein the water in the water system has a total hardness of 40 ppm orless CaCO₃; wherein the amino-acid based polymer adding step providesactive concentration of at least 3 ppm of the amino-acid based polymerin the volume of water in the water system; and wherein thehydroxyphosphonoacetic acid adding step provides active concentration ofat least 3 ppm of the hydroxyphosphonoacetic acid or its water solublesalt in the volume of water in the water system.
 7. The method of claim3 wherein the second phosphonic acid is HEDP, PBTC, or both.
 8. Themethod of claim 3 wherein the second phosphonic acid is HEDP and no PBTCis added to the water in the water system.
 9. The method of claim 8wherein the water in the water system contains a biocide.
 10. The methodof claim 9 wherein the biocide comprises chlorine or bromine and whereinthe water in the water system has (1) total hardness of 60 ppm or lessCaCO₃ or (2) a pH of 7-9.
 11. The method of claim 3 wherein the weightratio of the combined amino-acid based polymer andhydroxyphosphonoacetic acid or its water soluble salt to the secondphosphonic acid or its water soluble salt is 80:20 to 70:30.
 12. Themethod of claim 3 wherein (1) the water has a total hardness of 60 ppmor less CaCO₃ or (2) a pH of 7-9.
 13. The method of claim 3 wherein theactive amount of amino-acid based polymer added is equal to or greaterthan the active amount of the hydroxyphosphonoacetic acid or its watersoluble salt added; and wherein the active amount of amino-acid basedpolymer added is equal to or greater than the active amount of thesecond phosphonic acid or its water soluble salt added.
 14. The methodof claim 13 wherein the water (1) has a total hardness of 60 ppm or lessCaCO₃ or (2) a pH of 7-9.
 15. The method of claim 1 wherein theamino-acid based polymer is polyaspartic acid or a salt thereof andwherein the water in the water system contains a biocide.
 16. The methodof claim 1 wherein the first phosphonic acid is hydroxyphosphonoaceticacid or its water soluble salt; and wherein the amino-acid based polymerand hydroxyphosphonoacetic acid or its water soluble salt are combinedin a treatment composition prior to addition to the water system andwherein the treatment composition comprises around 2%-15% by weight ofthe amino-acid based polymer and around 2% to 10% by weight of thehydroxyphosphonoacetic acid or its water soluble salt, such that anactive amount of the amino-acid based polymer is equal to or greaterthan an active amount of the hydroxyphosphonoacetic acid or its watersoluble salt in the treatment composition.
 17. The method of claim 16further comprising adding an additional amount of the treatmentcomposition as needed to maintain an active concentration of theamino-acid based polymer of at least 3 ppm and an active concentrationof the hydroxyphosphonoacetic acid or its water soluble salt of at least3 ppm, wherein these concentrations are when added to a volume of waterin the water system; and wherein the water in the water system has atotal hardness of 60 ppm or less CaCO₃.
 18. The method of claim 1wherein the first phosphonic acid is hydroxyphosphonoacetic acid or itswater soluble salt; and the amino-acid based polymer,hydroxyphosphonoacetic acid or its water soluble salt, and a tracer arecombined in a treatment composition prior to addition to the watersystem and wherein the method further comprises: periodically measuringthe amount of treatment composition in the water system based on ameasurement of the tracer.
 19. The method of claim 18 wherein thetreatment composition further comprises one or more of a neutralizingamine, chlorine stabilizer, a scale inhibitor, a dispersion agent, asteel or copper corrosion inhibitor, chelants, and an azole corrosioninhibitor.
 20. The method of claim 18 wherein the treatment compositiondoes not include zinc or tin.
 21. The method of claim 1 wherein theamino-acid based polymer and hydroxyphosphonoacetic acid are both addedseparately to the water system.
 22. The method of claim 1 wherein noregulated metals are added to the water in the water system.
 23. Themethod of claim 1 wherein the water in the water system has a totalhardness of 120 ppm or less CaCO₃.
 24. The method of claim 23 whereinthe water in the water system has a pH of 7-9.
 25. The method of claim 1wherein the water in the water system contains a biocide and has totalhardness of 60 ppm or less CaCO₃.
 26. The method of claim 1 wherein theactive amount of amino-acid based polymer added is equal to or greaterthan the active amount of the first phosphonic acid or its water solublesalt added.
 27. The method of claim 1 wherein the water has a totalhardness of 60 ppm or less CaCO₃.
 28. The method of claim 1 wherein thewater has a total hardness of 40 ppm or less CaCO₃.